1. Field of the Invention
The present invention relates to a numerical control device which has the function of inputting a sinusoidal signal to a control loop of a numerical control device which controls a control object so as to calculate a frequency characteristic of the control loop of the numerical control device.
2. Description of the Related Art
In the past, a numerical control device which uses numerical values to control a machine tool which machines a workpiece has been known. A machine tool, for example, cuts, planes, drills, mills, grinds, or otherwise machines a workpiece and usually has built-in motors. Therefore, a motor control device which controls a motor of a machine tool by numerical values is a numerical control device in which the control object is a motor.
In a machine tool which uses a motor, the practice has been to measure the frequency characteristic (frequency response) of the motor which is connected to a load for the purpose of analysis of machine resonance as an inhibitory factor for improvement of characteristics and analysis of the response and stability of control. When measuring the frequency characteristic of a motor, the servo analyzer inputs a speed command of a sine wave into the numerical control device of the motor to which the load is connected while gradually raising the frequency. Further, a servo analyzer compares a motor speed which is obtained from a speed detector of the motor with a speed command and analyzes an amplitude ratio and phase difference. The results of measurement obtained by analysis of this servo analyzer is generally displayed as a Bode plot.
In this regard, with the method of inputting a sinusoidal signal to a speed loop of a numerical control device and calculating the frequency characteristic of the speed loop from the relationship of the input and the output, it is necessary to make the frequency gradually rise in the measurement band while performing the measurement, so there was the problem of a long measurement time. Therefore, a control device of a motor which excites the speed loop by white noise which includes the entire frequency of the speed loop and thereby eliminates the trouble of changing the frequency and enables measurement of the frequency characteristic in a short time is disclosed in Japanese Patent Publication No. 2000-278990A.
However, the control device of the motor which is disclosed in PLT 1 uses white noise as the signal which is input to the speed loop. Waveform changes in white noise depending on the generating pattern, so there is the issue that it is difficult to improve the measurement precision in the high frequency region.